The heart is the center of a person's circulatory system. It includes a complex electro-mechanical system performing two major pumping functions. The left portions of the heart draw oxygenated blood from the lungs and pump it to the organs of the body to provide the organs with their metabolic needs for oxygen. The right portions of the heart draw deoxygenated blood from the organs and pump it into the lungs where the blood gets oxygenated. These mechanical pumping functions are accomplished by contractions of the myocardium (heart muscles). In a normal heart, the sinoatrial (SA) node, the heart's natural pacemaker, generates electrical impulses, called action potentials, that propagate through an electrical conduction system to various regions of the heart to excite myocardial tissues in these regions. Coordinated delays in the propagations of the action potentials in a normal electrical conduction system cause the muscles in various regions of the heart to contract in synchrony such that the pumping functions are performed efficiently. The normal pumping functions of the heart, or the normal hemodynamic performance, require a normal electrical system to generate the action potentials and deliver them to designated portions of the myocardium with proper timing, a normal myocardium capable of contracting with sufficient strength, and a normal electro-mechanical association such that all regions of the heart are excitable by the action potentials.
Electrocardiography (ECG) is known to indicate the functions of the electrical system by allowing monitoring of the action potentials at various portions of the heart. Heart sounds, or generally energies resulted from the heart's mechanical vibrations, indicate the head's mechanical activities. Measurements performed with simultaneously recorded ECG and heart sounds provide for quantitative indications of the electro-mechanical association.
One type of heart sound, known as the third heart sound, or S3, can be used for assessment of heart failure status of a patient. A heart failure patient suffers from an abnormal electrical conduction system with excessive conduction delays and deteriorated heart muscles that result in asynchronous and weak heart contraction, and hence, reduced pumping efficiency, or poor hemodynamic performance. While the ECG of a heart failure patient may show excessive delays and/or blockages in portions of the electrical conduction system, S3 indicates his or her heart's abnormal mechanical functions. For example, an increase in S3 activity is known to be an indication of elevated filing pressures, which may result in a state of decompensated heart failure. Additionally, S3 amplitude is also related to filing pressures of the left ventricle during diastole. The pitch, or fundamental frequency, of S3 is related to ventricular stiffness and dimension. Chronic changes in S3 amplitude are correlated to left ventricular chamber stiffness and degree of restrictive filling. Such parameters indicate abnormal cardiac conditions, including degrees of severity, and need of appropriate therapies.
For these and other reasons, there is a need for detecting S3 in diagnosis, monitoring, and treatment of cardiac conditions including heart failure.